Laminated felted sheets and asbestos containing coating composition for use therein

ABSTRACT

Disclosed is a process for forming laminated felted sheets wherein a wet base sheet of fibrous material is formed on a paper making screen and, before the wet base sheet is removed from the screen, a nonseparable, uniform asbestos-binder composition is applied thereto. The composition comprises an intimitate mixture containing (a) at least 50 percent by weight of chrysotile asbestos having a specific surface area from about 60-80 m2/g., a magnetite content of from about 0.04-0.5 percent, a reflectance of from about 72-78 percent, and a pulpability such that 0.2-1 percent of the asbestos is retained on a 65 mesh Tyler screen and (b) a binder therefore. The ratio of asbestos to binder, on a dry weight basis, ranges from about 3:1 to 9:1.

United States Patent [72] Inventor Robert G. Woolery Lewiston,N.Y.

[2]] Appl. No. 796,913

[22] Filed Feb. 5, 1969 Continuation-impart of Ser. No. 576,248, Aug.31, 1966, abandoned [45] Patented Nov. 9, 1971 [73] Assignee UnionCarbide Corporation New York, N.Y.

[54] LAMINATED FELTED SHEETS AND ASBESTOS CONTAINING COATING COMPOSITIONFOR USE THEREIN 3 Claims, No Drawings [52] U.S.Cl 162/129, 117/28,117/140, 161/156, 161/205, 162/153, 162/ 155 [51] Int. Cl B32b 5/08,B32b 19/06, D21h 5/18 [50] Field of Search 162/3, 127, 129, 132, 133,153,201, 186; 161/155, 156,205; 117/140, 28, 126; 106/63 56] ReferencesCited UNITED STATES PATENTS 367,424 8/1887 162/129 2,993,802 7/1961Cascone 162/129 X 3,246,767 4/1966 Pall et a1. 1 17/140 X OTHERREFERENCES Paper Trade Journal (Feb. 14, 1966) pg. 40- 4, New Type ofAsbestos Shows Advantages in Papermuking lngalls et ul.

Pulp and Paper, Casey, James P., lnterscience Publishers, N.Y. 1961 p.1553- 4 Vol.3

Primary Examiner-S. Leon Bashore Assistant Examiner-Alfred D'Andrea, Jr.

Anorneys- Paul A. Rose, Thomas I. O'Brien, Frederick J. McCarthy, .Ir.,Robert C. Cummings and Lawrence G. Kastriner ABSTRACT: Disclosed is aprocess for forming laminated felted sheets wherein a wet base sheet offibrous material is formed on a paper making screen and, before the wetbase sheet is removed from the screen, a nonseparable, unifonn Thedesirability of adding a binder to nonwoven felted sheets has been knownfor a long time, and numerous binders have been used for this purpose,for example, natural and synthetic resins, gums starches, waxes andvarious rubbery lattices. In accordance with prior art methods thesebinders have been incorporated into the felted fibrous materials in oneof three ways. The most common way of incorporating the binder is to mixit with the fibrous furnish composition and then lay and dewater themixture on a conventional Fourdrinier screen or cylinder machine. Thistype of process suffers from a variety of difficulties, the mostimportant of which is improper coagulation and self-agglomeration of thebinder causing weakness and lack of uniformity in the paper.

Another way of incorporating binders into felted fibrous sheets has beenthe practice, disclosed, for example, in US. Pat No. 2,022,687, of firstforming a fibrous web upon a paper-making machine and thereafterimpregnating the web, while supported on the paper-making screen, bypassing it through a permeating bath containing the binder material.This practice suffers from the disadvantage of requiring a separatesaturating machine, as well as difficulty in controlling the amount ofbinder added to the original sheet. Neither of the above-describedmethods serves to produce a laminated or coated structure, but ratherproduces a more or less imperfectly impregnated sheet.

A laminated sheet can, of course, be made by simply coating the surfaceof finished paper with a rubber, resinous or waxy binder. Such products,however, tend to have poor adhesion between the coating and the paper.

It has long been desirable to produce a paper product which contains onat least one side thereof a coating of a binder which is integrallybound to and substantially inseparable from its paper base sheet, ie toproduce a laminated product wherein the lamina will not separate, and tobe able to apply such coating to the base sheet simply, economically andwithout the need for additional complex machinery.

OBJECTS It is an object of this invention to produce a coated nonwovenfelted fibrous sheet containing on at least one surface thereof asubstantially nonseparable uniform and smooth rubbery, resinous or waxycoating.

It is another object of this invention to provide a process for applyingto at least one surface of a felted fibrous base sheet, a resinous,rubbery or waxy coating by use of conventional paper-making machinery.

It is yet another object of this invention to produce a compositionsuitable for coating nonwoven felted fibrous base sheets, such as paperand the like, which coating will be integrally bonded to said base sheetand form a uniform, smooth coating thereon.

DESCRIPTION OF INVENTION The above mentioned and other objects whichwill become apparent from the detailed description to follow areachieved by a process comprising the steps of l providing a base sheetof felted fibrous material on a paper-making screen, and prior toremoval of said base sheet from the screen, (2) applying on top of saidbase sheet a composition comprising an intimate mixture of chrysotileasbestos fibers having certain critical properties (hereafter defined)and a binder therefor.

Another aspect of this invention consists of a laminated productconsisting essentially of a felted fibrous base sheet and integrallybonded thereto a coating or lamina; the latter comprising an intimatemixture of chrysotile asbestos having certain critical properties(hereafter defined) and a binder therefor.

A third aspect of this invention consists of a composition, suitable forcoating nonwoven felted sheets, comprising an intimate mixture ofchrysotile asbestos fibers having certain critical properties (hereafterdefined) and a binder therefor. Said composition, which may also be usedto form a self-supporting sheet, may if desired, include optionalingredients such as conventional paper-making fibers, fillers, pigments,dyes and the like.

To be suitable for purposes of this invention the asbestos used musthave the following critical properties:

specific surface area 60-80 m./g. Magnetite content 004-0051 Reflectance7278% Pulpability 0.24.095

Asbestos having the aforementioned properties is commercially availableas high purity grade Calidria* Trademark of Union Carbide Corp.asbestos.

The properties of the asbestos material set forth above are critical inthe sense that only by use thereof are the desired results of theinvention obtained.

Specific surface area is calculated from adsorption data using the BET(Brunauer, Emmet, Teller) method as described in Brunauer, TheAdsorption of Gases and Vapors, Princeton University Press 1945).

Magnetite content is measured by a permeametric device patterned afterASTM standard method D-l I 18-57. Since the lower limit of detection ofthe ASTM device is only about 0.20 percent magnetite, the ASTM methodhas been im proved with respect to sensitivity to measure a limit ofdetection of 0.005 percent magnetite, and the range of measurements hasbeen extended to measure 0.10 percent magnetite in the midscale of theinstrument. In order to obtain this greater range and improvedsensitivity, the ASTM method has been modified to detect the phasechanges of the current generated when magnetic materials are placed inthe transfomier core rather than the voltage changes generated.

Reflectance is measured on a sample prepared according to TAPPI(Technical Association of the Pulp and Paper Industry) standardT-452-m-58 and is reported as percent of ultimate reflectance based onmagnesium oxide as the standard of percent reflectance.

The pulpability of the high purity asbestos must be such that less than1.0 percent and preferably less than 0.5 percent is retained on a65-mesh Tyler screen when measured in accordance with the proceduredescribed below. The term +65 -mesh is used tomean the amount, expressedas the percent of the sample, which does not pass through but isretained on a 65-mesh Tyler screen. The measurements are made on a wetpulped sample rather than a dry sample, since the particle size underwet pulped conditions is significant for purposes of paper manufacture.The pulpability is determined by adding 40 g. of asbestos and 2 litersof water to a TAPPl Standard Disintegrator and agitating the mixture for4 minutes. A 250 ml. aliquot sample is then taken from the disintegratorand diluted to 3 liters with water. The diluted slurry is then pouredthrough a 65-mesh (Tyler standard) wire screen held at an angle of about30 from the horizontal position. The oversize remaining on the screen iswashed back into a 4 liter beaker diluted with water and poured throughthe screen again as before. The oversize remaining is then backwashed,diluted and poured over the screen a third time. The oversize remainingis then dried at about 50 C. and weighed. The net weight of the oversizemultiplied by 20 is the percent +65-mesh asbestos material contained inthe original sample. This is the value referred to as the Pulpability."

Table I below illustrates the differences in the properties of theclosest chrysotile asbestos of the prior art and the chrysotile asbestosessential for use in the present invention. Although Coalingachrysotile* asbestos is preferred as the source of the asbestos, anychrysotile asbestos is suitable *Coalinga chrysotile asbestos is minedfrom a large deposit near Cooling. California.

TABLE I.COMPARATIVE PHYSICAL PROPERTIES OF ASBESTOS FIBERS Pulpabilitypercent Specific Percent surface magnetits Percent reflectance area,

Type of asbestos rnJ/gm. mesh Canadian chrysotile Conventional coaiingachrysotile Required for invention Binders which are useful in thepreparation of the coating composition of this invention include all ofthe common sizing agents used in the paper industry, such as animalglues, starches, gelatin, rosin, rosin derivatives, waxes, bituminousmaterials such as asphalts, tars, pitches and bituminous as well asresinous and rubbery lattices.

Synthetic, resinous and rubbery lattices are the preferred binders.Illustrative suitable rubbery lattices are copolymers of butadiene andstyrene (i.e. GR-S rubber containing 50-80 percent by weight butadiene),copolymers of butadiene and acrylonitrile (i.e. Buna-Nor Hycar rubbercontaining 50-80 percent butadiene), polychloroprenes (i.e. neoprenes),homopolymers of butadiene, butadiene-isoprene copolymers, andterpolymers of butadiene, styrene and acrylic acid or lower alkylacrylites.

illustrative resinous binders which are useful are thermosetting resinssuch as phenol aldehyde resins, and melamine formaldehyde resins.Suitable thermoplastic resin binders include, for example, vinyl andsubstituted vinyl resins such as polyvinylchloride, polyvinylacetate,polyvinylacetal, polyvinylalcohol, polystyrene, polyacrylates,polymethacrylates, polyacrylonitrile, polyacrylamide and copolymers ofthese materials. Any resinous binder is useful for depositing theasbestos of this invention onto a base sheet, as long as it isdispersible in an aqueous medium or suspendible therein in particulateform.

The coating composition is prepared by first dispersing the asbestos inan aqueous slurry by means of a high shear device; for example, a Reitzdisintegrator, a Fitzmill or a Waring blender. The binder, usually in anaqueous suspension, is then blended in with the asbestos using low shearmixing such as obtained with an ordinary mixer.

The concentrations of both the asbestos slurry and the binder suspensionare ordinarily kept below about 3 percent solids by weight, since athigher concentrations the composition becomes too viscous for easyhandling. The proportions of asbestos to binder are controlled to giveoptimum efficiency in terms of the retention of the solids on thepaper-making screen. The asbestos content, however, must be sufficientlyhigh to insure that its cationic charge will be adequate to coflocculateall the other solid components of the mixture. If the concentration ofthe binder is too high, the binder in excess of that which the asbestoscan flocculate will in large part be lost by draining through the basesheet into the white water. The optimum proportions of asbestos tobinder will vary depending upon the particular binder and otheradditives used. Preferably, the ratio of asbestos to binder (on a dryweight basis) is from 3:1 to 9:1. The same proportions are usefulwhether the composition is to be used for coating purposes or for makingan extruded, self-supporting film. Self-supporting films of thiscomposition have the properties of an asbestos filled plastic film, andcan be used, for example, as packaging film or as wallpaper.

The asbestos-binder coating composition may contain additives such asfillers, pigments or fibrous materials. The use of TiO and clay areillustrated below, however, any conventional paper making fillers and/orpigments may be used, as well as mixtures thereof. Furthermore, fibrousmaterials other than asbestos, both synthetic and natural, may also beincluded, if desired, in the coating composition. For example, one ormore natural or synthetic mineral or vegetable fibers may be added tothe composition. in all such cases, however, the weight of asbestoshaving the critical characteristics previously described must be atleast 50 percent of the weight in the composition. The asbestos in sucha coating composition is believed to act as a coupling agent between thebinder and the other fiber or nonfibrous additives, since the cationicnature of the asbestos is believed to be attracted by the other fibers,the nonfibrous additives, as well as the latex binder, all of which areanionic in character. The binder is preferably added after the asbestosand additive have been adequately mixed, since the asbestos will causethe binder to coagulate.

The asbestos-binder composition of this invention is novel and unusualin that it can be applied directly on top of a wet base sheet before thesheet is taken ofi' the paper-making screen. Such on the wire coating"has not previously been feasible because coating formulations tried inthe past have drained through the base sheet. Use of asbestos having thecritical properties previously defined holds out the coating compositionfrom the base sheet, and enables the binder composition to be applieddirectly onto the paper making screen containing the wet base sheet.Furthermore, there is no need for using organic surfactants, wettingagents, dispersing agents, or other fiocculating agents required byprior art methods to obtain flocculation and deposition of a binder ontothe fibers. The critical properties of the above described asbestositself assure both proper cofiocculation of the binder onto the asbestosand deposition of the asbestos-binder coating onto the base sheet.

Any felted product which can be prepared on a paper making screen can beused as the base sheet in the present invention. These felted productscan be formed from organic, inorganic or mixed materials. Paper basesheets are preferred. As used throughout the specification and claims ofthis disclosure the term paper" is used in its generic sense, i.e. toinclude any nonwoven, felted fibrous sheet, including but not restrictedto bond, wrapping, tissue, printing, wall and backing paper as well ascardboard, wallboard, millboard, and the like.

Suitable inorganic fibrous materials for base sheets include glass wool,mineral wool, and silicate fibers. Useful organic fibers include, forexample, cotton, silk, hemp, ramie, alpaca, hair, fur and animalbristles. Useful synthetic organic fibers are fibers made frompolyamides, acrylates, polyesters, cellulose acetate, regeneratedcellulose (rayon), polyvinyl chloride, polyethylene, polyurethane,polytetrafluoroethylene and the like.

Preferred base sheets are those made from conventional cellulosic pulpused for the manufacture of paper for example, mechanical, semichemical,sulfite, sulfate, or craft (soda) pulp. Mixtures of cellulosic pulp ormixtures of cellulosic and noncellulosic fibers may also be used.

The paper base sheet useful in this invention may have included in itconventional fillers such as, for example, clay, sodium silicoaluminate,diatomaceous silica, calcium silicate, talc, calcium carbonate, calciumsulfate, barium sulfate, zinc sulfate and titanium dioxide. Such fillersmay be incorporated not only into the base sheet, but also into theasbestos coating composition of this invention, if desired.

In general, a base sheet is made by first preparing a dilute aqueouspulp of suspended fibers, incorporating into the pulp desired additivessuch as fillers or pigments to make a paper furnish composition,depositing the furnish composition from a head box onto a moving finemesh screen, and then draining the excess water through the screen. Theasbestos-binder coating composition of this invention is then applieddirectly onto the wet felted fibrous web or sheet while the latter isstill moving on the paper making screen. The coating step isconveniently carried out by having a second head box from which thecoating composition is applied onto the wet base-covered screen.

sheet with a coating of asbestos and binder were prepared on alaboratory Noble and Wood handsheet machine using the folground wood andsulfate was 250. The only additive used in the base sheet furnish wasalum, added in sufficient amount to give a pH of 4.5 at the firstheadbox. The first headbox contained the furnish composition for thebase sheet, and the lowing procedure. A base sheet having a basis weightof 60 secondafy headbox contained the coating composition for the g./mwas first prepared by adding unbleached craft pulp to cop e the decklebox of the handsheet machine and allowing it to Three dliferem fumlsheswere used m the Secondary headdrain almost completely. Then a secondcompositionconsistbox for laynig down e Ply of the l P The first ing ofa mixture of binder and asbestos having the critical protop ply coatingcomposmon labeled composmon A m table perties heretofore defined waspoured on top of the base sheet below conslsted of 85 percent e andPercent i e which was Sm] in the deckle The proportions (on a dry Thesecond top ply coating composition, labeled composition weight basis) ofasbestos to binder used are given in table n B in table Ill below,consisted of 40 percent asbestos, 40 perbelow. in examples 1 through 7the binder used was an aque- F F and e f T th'rd P P eoatlhg ousdispersion of a Synthetic late of a copolymel. containing 1 5 position,labeled composition Cm table 1" below, consisted of about 60 percentstyrene and 40 percent butadiene. in exam- Percent asbestos Pe ahd 20peleeht latexples 8 through 12 the binder used was an aqueous dispersionof 8 composmohs were PP h 1 Percent of a copolymer containing about 40percent styrene, 5 percent Sends Slumes directly onto he wet ba5e sheetas it moved acrylic acid and 55 percent ethylhexyl acrylate. Theasbestos tmuoiisly along theFourdnhler wire The asbestos used had latexcoating composition contained about 1 percent solids. it 20 the emlealProperties e forth above- In all cases l was added to the deckle boxslowly in order to minimize the used was an aqueous dlspersloh of a p yfeomalhlhg disturbance of the wet cellulosic base sheet. The deckle boxabout 60 Pe e styrene 40 h huadlehe was then allowed to draincompletely. The laminated sheet one objective of this senes ofexperimental e was [0 was then removed from the deckle box, pressed witha felt T the P layer as heavy as posslble and to PP Onto press, anddried in a drum dryer operated at a temperature of hght base ehee as asOnto a heavy base Sheet- Changes in about 105 C. The heat of the driernot only dried the the thlekhese of both the top P y and the hotmm P ywere l i d sheet b l cured h l made by setting the flow rate from aheadbox at a steady rate Twelve Samples were prepared i the mannerdescribed and then ad usting the speed of the Fourdrinier wire. Once aabove and tested to determine optimum retention of the coatbase Ph hadbeen long enough to insure Steady State ing, as well as the physicalproperties of the laminates 3 Conditions the flow of 1 P y furnish wasstarted from the produced. second headbox and increased slowly until thewet web ap- The data from table ll demonstrates that optimum retention Pto be j the verge of break g een the uch of the coating is achieved whenthe ratio of asbestos to latex roll n the fir preSS- nder theseconditions the run was (on a dry weight basis) is from 80:20 to 90:10,in other words, continued for 10 to 15 minutes. Thereafter the wirespeed was when about 10-20 percent of the asbestos latex composition isg and the Procedure repeated with a different P p y latex and 80-90percent is asbestos. The data above also ling f rni hdemonstrates thatin general the best physical properties are Samples of paper were takenfrom each set of runs and cut obtained when there is maximum retentionof the coating. into sheets. Some Of the sheets from each set werecalendered at room temperature and some at approximately 230 F. AfterEXAMPLES 13-22 40 conditioning at a constant temperature and humidityroom The following examples demonstrate the method of making criticalwax tests were made on the calendered sheets, as well a two-ply l m n ppe in accordance with the invention, as on uncalendered samples ofsheet. The results of the critical on a continuous paper-making machineby using a secondary wax tests are shown in table Ill below. head box ona conventional Fourdrinier machine. The base The critical wax tests wereconducted in accordance with sheets were TAPPI standard test T-459six-65. This test consists of taking TABLE II Tensile Top strength H2OOil Ratio of laminate Percent adsorpadsporasbestos retention reflec- DryWet tion a on 4 to latex (percent) l tapes 1 (lbs.) (oz) (minutes)(minutes) 1 Top laminate retention is the percent asbestos-latexretained based on the quantity applied to the base sheet.

2 Percent reflectance was determined with a photovolt meter according toTAPPI standards.

3 H2O adsorption was determined by placing a drop of water on thesurface of the sheet and recording the time in minutes for the water tobe adsorbed.

of oil.

made from a furnish containing 50 percent wood and 50 percent bleachedsoft wood sulfate pulp. The sulfate pulp was a standard series of waxsticks, each having a different tackine'ss. heating them to theirmelting point and then applying refined to a freencss of 370 and thefreeness of the mixture of 75 ea h f the sticks to the paper sheet, Thnumber f 1 TABLE III Critical wax number Weight Galen Basis ratio daredHot Top Wei ht. top ply: room calenply (gmirm) base plyUncalontemperacred ered ture F.

A 117 .86 6 6 7 B 154 81 7 l0 11 B 100 35 6 9 B 126 91 6 8 11 B 88 76 77 10 B 105 1. 06 8 9 10 C 109 .36 10 10 C 88 .33 10 10 11 C 69 35 8 9 10C 79 .20 S 9 10 highest numbered stick that does not pull fibers fromthe surface is the critical wax value of the paper. It can be seen fromtable Ill that very good bonding between the plies was obtained asindicated by the critical wax numbers ranging from 6 to l 1 Someincrease in critical wax was obtained by calendering the sheet, with hotcalendering giving the best results. The tests also indicate that anincrease in the ratio of latex to asbestos and pigment increases plybonding.

The laminated paper of the present invention has numerous advantages notpossessed by prior art materials, such as improved ply bonding and lowcost of manufacture due to the fact that separate equipment for coatingis not required. The coated paper of the present invention isparticularly useful for one side hold out items such as paper plates,drinking cups, flexible packaging and the like.

I claim:

1. A process for the manufacture of laminated sheets comprising thesteps of:

l. forming on a paper making screen, a wet base sheet of felted fibrousmaterial and prior to removal of said base sheet from said screenproviding a nonseparable, uniform, asbestos-binder coating on thesurface of said base sheet by applying on top of said wet base sheetbefore said wet base sheet is removed from the paper-making screen acomposition comprising an intimate mixture containing at least 50percent by weight of chrysotile asbestos characterized by a specificsurface area between about 60 to m/gm., a magnetite content of fromabout 0.04 to 0.5 percent, a reflectance of about 72 to 78 percent and apulpability such that 0.2 to 1 percent of the asbestos is retained on a(SS-mesh Tyler screen and a binder therefor, the ratio of asbestos tobinder, on a dry weight basis, being from about 3: l to 9: 1.

2. The process of claim 1 wherein the coating composition applied on topof said base sheet contains an additive selected from the groupconsisting of fibrous materials, fillers, pigments and mixtures thereof.

3. The process of claim 1 wherein the base sheet is paper.

2. providing a nonseparable, uniform, asbestos-binder coating on thesurface of said base sheet by applying on top of said wet base sheetbefore said wet base sheet is removed from the paper-making screen acomposition comprising an intimate mixture containing at least 50percent by weight of chrysotile asbestos characterized by a specificsurface area between about 60 to 80 m2/gm., a magnetite content of fromabout 0.04 to 0.5 percent, a reflectance of about 72 to 78 percent and apulpability such that 0.2 to 1 percent of the asbestos is retained on a65-mesh Tyler screen and a binder therefor, the ratio of asbestos tobinder, on a dry weight basis, being from about 3:1 to 9:1.
 2. Theprocess of claim 1 wherein the coating composition applied on top ofsaid base sheet contains an additive selected from the group consistingof fibrous materials, fillers, pigments and mixtures thereof.
 3. Theprocess of claim 1 wherein the base sheet is paper.